[manuc]

Hello All
I am doing a conjugate heat transfer problem with 2 regions:
1. Air
2. plate

The issue I face
The initial pressure residual doesn't change

Region: air Courant Number mean: 0.025093108 max: 0.40052825
Region: plate Diffusion Number mean: 3.7111592e-07 max: 7.8177845e-07
deltaT = 0.0071130688
Time = 5.8941


Solving for fluid region air
DILUPBiCG:  Solving for T, Initial residual = 0.0015977895, Final residual = 7.1757907e-08, No Iterations 2
max(T) [0 0 0 1 0 0 0] 307.07585
GAMG:  Solving for p_rgh, Initial residual = 0.29225662, Final residual = 0.00014979926, No Iterations 5
time step continuity errors : sum local = 5.6147294e-07, global = -3.626898e-21
GAMG:  Solving for p_rgh, Initial residual = 0.29228288, Final residual = 0.0001558772, No Iterations 5
time step continuity errors : sum local = 5.8412794e-07, global = 1.6563367e-21
GAMG:  Solving for p_rgh, Initial residual = 0.29228292, Final residual = 0.0001561875, No Iterations 5
time step continuity errors : sum local = 5.8528492e-07, global = -1.0209638e-20

Solving for solid region plate
DICPCG:  Solving for T, Initial residual = 0.00033675569, Final residual = 1.8134589e-10, No Iterations 1
Min/max T:min(T) [0 0 0 1 0 0 0] 299.77487 max(T) [0 0 0 1 0 0 0] 300.23137

Solving for fluid region air
DILUPBiCG:  Solving for T, Initial residual = 0.00086688609, Final residual = 5.8887298e-08, No Iterations 2
max(T) [0 0 0 1 0 0 0] 307.07154
GAMG:  Solving for p_rgh, Initial residual = 0.28837172, Final residual = 0.00025808741, No Iterations 5
time step continuity errors : sum local = 9.6388206e-07, global = -3.7600441e-21
GAMG:  Solving for p_rgh, Initial residual = 0.28839029, Final residual = 0.00026193496, No Iterations 5
time step continuity errors : sum local = 9.7833528e-07, global = 2.6948758e-21
GAMG:  Solving for p_rgh, Initial residual = 0.28839033, Final residual = 0.00026213134, No Iterations 5
time step continuity errors : sum local = 9.7907289e-07, global = -2.6309657e-21

Solving for solid region plate
DICPCG:  Solving for T, Initial residual = 7.843695e-07, Final residual = 7.843695e-07, No Iterations 0
Min/max T:min(T) [0 0 0 1 0 0 0] 299.7751 max(T) [0 0 0 1 0 0 0] 300.23089

Solving for fluid region air
DILUPBiCG:  Solving for T, Initial residual = 0.00047949062, Final residual = 3.5964391e-08, No Iterations 2
max(T) [0 0 0 1 0 0 0] 307.06885
GAMG:  Solving for p_rgh, Initial residual = 0.28572757, Final residual = 0.0002516689, No Iterations 6
time step continuity errors : sum local = 9.4478046e-07, global = -6.5188299e-21
GAMG:  Solving for p_rgh, Initial residual = 0.28574053, Final residual = 0.00025317592, No Iterations 6
time step continuity errors : sum local = 9.5044118e-07, global = 4.7719539e-21
GAMG:  Solving for p_rgh, Initial residual = 0.28574058, Final residual = 0.00025325281, No Iterations 6
time step continuity errors : sum local = 9.5072952e-07, global = 3.728089e-22

Solving for solid region plate
DICPCG:  Solving for T, Initial residual = 1.2740441e-06, Final residual = 6.9627797e-13, No Iterations 1
Min/max T:min(T) [0 0 0 1 0 0 0] 299.77523 max(T) [0 0 0 1 0 0 0] 300.23051

Solving for fluid region air
DILUPBiCG:  Solving for T, Initial residual = 0.0002695116, Final residual = 2.4592606e-08, No Iterations 2
max(T) [0 0 0 1 0 0 0] 307.06714
GAMG:  Solving for p_rgh, Initial residual = 0.2840107, Final residual = 0.00027359005, No Iterations 6
time step continuity errors : sum local = 1.0255247e-06, global = 1.0332132e-21
GAMG:  Solving for p_rgh, Initial residual = 0.28401878, Final residual = 0.00027452449, No Iterations 6
time step continuity errors : sum local = 1.0290257e-06, global = 7.5413915e-21
GAMG:  Solving for p_rgh, Initial residual = 0.28401879, Final residual = 0.00027457255, No Iterations 6
time step continuity errors : sum local = 1.0292054e-06, global = 1.4401075e-20

Solving for solid region plate
DICPCG:  Solving for T, Initial residual = 2.5904077e-07, Final residual = 2.5904077e-07, No Iterations 0
Min/max T:min(T) [0 0 0 1 0 0 0] 299.77529 max(T) [0 0 0 1 0 0 0] 300.23051

Solving for fluid region air
DILUPBiCG:  Solving for T, Initial residual = 0.00014960406, Final residual = 6.311792e-07, No Iterations 1
max(T) [0 0 0 1 0 0 0] 307.06612
GAMG:  Solving for p_rgh, Initial residual = 0.28286788, Final residual = 0.00019960496, No Iterations 7
time step continuity errors : sum local = 7.4439393e-07, global = -5.7732121e-21
GAMG:  Solving for p_rgh, Initial residual = 0.28287327, Final residual = 0.00020010332, No Iterations 7
time step continuity errors : sum local = 7.4626443e-07, global = -2.5670556e-21
GAMG:  Solving for p_rgh, Initial residual = 0.28287328, Final residual = 0.00020013241, No Iterations 7
time step continuity errors : sum local = 7.4637356e-07, global = 5.006291e-21

Solving for solid region plate
DICPCG:  Solving for T, Initial residual = 4.0860369e-07, Final residual = 4.0860369e-07, No Iterations 0
Min/max T:min(T) [0 0 0 1 0 0 0] 299.77533 max(T) [0 0 0 1 0 0 0] 300.2305

Solving for fluid region air
DILUPBiCG:  Solving for T, Initial residual = 8.915537e-05, Final residual = 7.1263867e-07, No Iterations 1
max(T) [0 0 0 1 0 0 0] 307.06574
GAMG:  Solving for p_rgh, Initial residual = 0.2821784, Final residual = 0.00020594294, No Iterations 7
time step continuity errors : sum local = 7.6754809e-07, global = 1.5231907e-21
GAMG:  Solving for p_rgh, Initial residual = 0.28218178, Final residual = 0.0002062782, No Iterations 7
time step continuity errors : sum local = 7.6880604e-07, global = 3.6428755e-21
GAMG:  Solving for p_rgh, Initial residual = 0.28218178, Final residual = 0.00020629814, No Iterations 7
time step continuity errors : sum local = 7.6888083e-07, global = 1.3793929e-20

Solving for solid region plate
DICPCG:  Solving for T, Initial residual = 4.5828655e-07, Final residual = 4.5828655e-07, No Iterations 0
Min/max T:min(T) [0 0 0 1 0 0 0] 299.77536 max(T) [0 0 0 1 0 0 0] 300.2306

Solving for fluid region air
DILUPBiCG:  Solving for T, Initial residual = 4.7827065e-05, Final residual = 2.2985107e-07, No Iterations 1
max(T) [0 0 0 1 0 0 0] 307.06551
GAMG:  Solving for p_rgh, Initial residual = 0.28171533, Final residual = 0.00020993592, No Iterations 7
time step continuity errors : sum local = 7.8213501e-07, global = -9.3521776e-21
GAMG:  Solving for p_rgh, Initial residual = 0.2817176, Final residual = 0.00021015795, No Iterations 7
time step continuity errors : sum local = 7.8296837e-07, global = -4.0582912e-21
GAMG:  Solving for p_rgh, Initial residual = 0.28171761, Final residual = 0.00021017166, No Iterations 7
time step continuity errors : sum local = 7.830198e-07, global = 3.5363587e-21

Solving for solid region plate
DICPCG:  Solving for T, Initial residual = 4.9787724e-07, Final residual = 4.9787724e-07, No Iterations 0
Min/max T:min(T) [0 0 0 1 0 0 0] 299.77538 max(T) [0 0 0 1 0 0 0] 300.23065

Solving for fluid region air
DILUPBiCG:  Solving for T, Initial residual = 2.6090939e-05, Final residual = 1.1814457e-07, No Iterations 1
max(T) [0 0 0 1 0 0 0] 307.06537
GAMG:  Solving for p_rgh, Initial residual = 0.28140271, Final residual = 0.00021239068, No Iterations 7
time step continuity errors : sum local = 7.9111348e-07, global = -2.417932e-21
GAMG:  Solving for p_rgh, Initial residual = 0.28140414, Final residual = 0.00021253976, No Iterations 7
time step continuity errors : sum local = 7.9167325e-07, global = 1.5657974e-21
GAMG:  Solving for p_rgh, Initial residual = 0.28140414, Final residual = 0.00021254929, No Iterations 7
time step continuity errors : sum local = 7.9170899e-07, global = 1.101384e-20

Solving for solid region plate
DICPCG:  Solving for T, Initial residual = 5.222418e-07, Final residual = 5.222418e-07, No Iterations 0
Min/max T:min(T) [0 0 0 1 0 0 0] 299.77539 max(T) [0 0 0 1 0 0 0] 300.23068

Solving for fluid region air
DILUPBiCG:  Solving for T, Initial residual = 1.4511823e-05, Final residual = 6.5523126e-08, No Iterations 1
max(T) [0 0 0 1 0 0 0] 307.06528
GAMG:  Solving for p_rgh, Initial residual = 0.28119291, Final residual = 0.00021391702, No Iterations 7
time step continuity errors : sum local = 7.9670066e-07, global = -9.3841326e-21
GAMG:  Solving for p_rgh, Initial residual = 0.28119381, Final residual = 0.00021401911, No Iterations 7
time step continuity errors : sum local = 7.9708407e-07, global = -1.1716851e-22
GAMG:  Solving for p_rgh, Initial residual = 0.28119381, Final residual = 0.00021402582, No Iterations 7
time step continuity errors : sum local = 7.9710924e-07, global = -5.677347e-21

Solving for solid region plate
DICPCG:  Solving for T, Initial residual = 5.3730343e-07, Final residual = 5.3730343e-07, No Iterations 0
Min/max T:min(T) [0 0 0 1 0 0 0] 299.77539 max(T) [0 0 0 1 0 0 0] 300.23069

Solving for fluid region air
DILUPBiCG:  Solving for T, Initial residual = 1.8336375e-05, Final residual = 3.3775715e-07, No Iterations 1
max(T) [0 0 0 1 0 0 0] 307.06515
GAMG:  Solving for p_rgh, Initial residual = 0.03702251, Final residual = 3.052687e-05, No Iterations 11
time step continuity errors : sum local = 3.3549545e-07, global = 1.0332132e-21
GAMG:  Solving for p_rgh, Initial residual = 0.036786632, Final residual = 2.849982e-05, No Iterations 11
time step continuity errors : sum local = 3.1319121e-07, global = -4.0582912e-21
GAMG:  Solving for p_rgh, Initial residual = 0.036785243, Final residual = 9.9930364e-08, No Iterations 31
time step continuity errors : sum local = 1.0904319e-09, global = 6.4053853e-21

Solving for solid region plate
DICPCG:  Solving for T, Initial residual = 5.5942857e-07, Final residual = 5.5942857e-07, No Iterations 0
Min/max T:min(T) [0 0 0 1 0 0 0] 299.7754 max(T) [0 0 0 1 0 0 0] 300.2307
ExecutionTime = 9340.47 s  ClockTime = 9355 s


Region: air Courant Number mean: 0.025087667 max: 0.40051174
Region: plate Diffusion Number mean: 3.7061104e-07 max: 7.8071489e-07
deltaT = 0.0071039405
Time = 5.9012

What is observed
1. There are 10 outercorrectors (though number of pimple iteration not displayed) and 3 ncorrectors in each loop.
2. No change in p_rgh initial residual found till the last outer loop
3.Sudden jump of p_rgh initial residual from [/b] 0.28[/b] to 0.03 (see code snippet)

 Solving for solid region plate
DICPCG:  Solving for T, Initial residual = 5.222418e-07, Final residual = 5.222418e-07, No Iterations 0
Min/max T:min(T) [0 0 0 1 0 0 0] 299.77539 max(T) [0 0 0 1 0 0 0] 300.23068

Solving for fluid region air
DILUPBiCG:  Solving for T, Initial residual = 1.4511823e-05, Final residual = 6.5523126e-08, No Iterations 1
max(T) [0 0 0 1 0 0 0] 307.06528
GAMG:  Solving for p_rgh, Initial residual = 0.28119291, Final residual = 0.00021391702, No Iterations 7
time step continuity errors : sum local = 7.9670066e-07, global = -9.3841326e-21
GAMG:  Solving for p_rgh, Initial residual = 0.28119381, Final residual = 0.00021401911, No Iterations 7
time step continuity errors : sum local = 7.9708407e-07, global = -1.1716851e-22
GAMG:  Solving for p_rgh, Initial residual = 0.28119381, Final residual = 0.00021402582, No Iterations 7
time step continuity errors : sum local = 7.9710924e-07, global = -5.677347e-21

Solving for solid region plate
DICPCG:  Solving for T, Initial residual = 5.3730343e-07, Final residual = 5.3730343e-07, No Iterations 0
Min/max T:min(T) [0 0 0 1 0 0 0] 299.77539 max(T) [0 0 0 1 0 0 0] 300.23069).

I am not able to find why its happening ( Its observed in all time steps)
4. The prgh_initial value never changes in 1 outer iteration (see the specific region below)

Solving for solid region plate
DICPCG:  Solving for T, Initial residual = 5.222418e-07, Final residual = 5.222418e-07, No Iterations 0
Min/max T:min(T) [0 0 0 1 0 0 0] 299.77539 max(T) [0 0 0 1 0 0 0] 300.23068

Solving for fluid region air
DILUPBiCG:  Solving for T, Initial residual = 1.4511823e-05, Final residual = 6.5523126e-08, No Iterations 1
max(T) [0 0 0 1 0 0 0] 307.06528
GAMG:  Solving for p_rgh, Initial residual = 0.28119291, Final residual = 0.00021391702, No Iterations 7
time step continuity errors : sum local = 7.9670066e-07, global = -9.3841326e-21
GAMG:  Solving for p_rgh, Initial residual = 0.28119381, Final residual = 0.00021401911, No Iterations 7
time step continuity errors : sum local = 7.9708407e-07, global = -1.1716851e-22
GAMG:  Solving for p_rgh, Initial residual = 0.28119381, Final residual = 0.00021402582, No Iterations 7
time step continuity errors : sum local = 7.9710924e-07, global = -5.677347e-21

Solving for solid region plate
DICPCG:  Solving for T, Initial residual = 5.3730343e-07, Final residual = 5.3730343e-07, No Iterations 0
Min/max T:min(T) [0 0 0 1 0 0 0] 299.77539 max(T) [0 0 0 1 0 0 0] 300.23069

What did I try
1. Changing outercorrector and inner corrector numbers (no change observed)

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  2.4.0                                 |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    location    "system";
    object      fvSolution;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

solvers
{
    p_rgh
    {
        solver           GAMG;
        tolerance        1e-7;
        relTol           1e-3;

        smoother         GaussSeidel;

        cacheAgglomeration  true;
        nCellsInCoarsestLevel 10;
        agglomerator     faceAreaPair;
        mergeLevels      1;
    }

    p_rghFinal
    {
        $p_rgh;
        tolerance        1e-7;
        relTol           0;
    }



    "(U|T|k|epsilon|R)"
    {
        solver          PBiCG;
        preconditioner  DILU;
        tolerance       1e-6;
        relTol          0.0001;
    }

    "(U|T|k|epsilon|R)Final"
    {
        $U;
        relTol          0;
    }
}

PIMPLE
{
    momentumPredictor no;
    nOuterCorrectors 10;//tried 20 aswell no change
    nCorrectors    3;
    nNonOrthogonalCorrectors 0;
    pRefPoint (0.5 0.01 0);
    pRefValue       0;
    
}

relaxationFactors
{
    fields
    {
    p_rgh           0.2;
    }
    equations
    {
           U               0.3;
           T               0.5;
        "(k|epsilon|R)" 0.7;
        "(U|T|k|epsilon|R)Final" 1;
    }
}

// ************************************************************************* //

2. Tried changing solver for p_rgh to PCG

solvers
{
    p_rgh
    {
        solver          PCG;
        preconditioner  DIC;
        tolerance       1e-8;
        relTol          1e-3;
    }

    p_rghFinal
    {
        $p_rgh;
        relTol          0;
    }

3. Tried changing fvSchemes from linear to upwind
fvsolution 1

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  1.7.1                                 |
|   \\  /    A nd           | Web:      www.OpenFOAM.com                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      fvSchemes;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

ddtSchemes
{
    default Euler; // steadyState; //
}

gradSchemes
{
    default         Gauss linear;
}

divSchemes
{
    default         none;
    div(phi,U)      Gauss linear ;
    div(phi,h)      Gauss linear limited 0.333;
    div(phi,k)      Gauss linear limited 0.333;
    div(phi,T)      Gauss linear limited 0.333;
    div(phi,epsilon) Gauss linear limited 0.333;
    div(phi,R)      Gauss linear;
    div(R)          Gauss linear;
    div((muEff*dev2(grad(U).T()))) Gauss linear;
    div(U,p)        Gauss upwind;
    div((nuEff*dev(grad(U).T()))) Gauss linear;
   div((nuEff*dev(T(grad(U))))) Gauss linear;
}

laplacianSchemes
{
    default         Gauss linear uncorrected;
    laplacian(muEff,U) Gauss linear limited 0.333;
    laplacian((rho*(1|A(U))),p_rgh) Gauss linear limited 0.333;
    laplacian((1|A(U)),p) Gauss linear corrected;
    laplacian(alphaEff,h) Gauss linear limited 0.333;
    laplacian(DkEff,k) Gauss linear limited 0.333;
    laplacian(DepsilonEff,epsilon) Gauss linear limited 0.333;
    laplacian(DREff,R) Gauss linear limited 0.333;
    laplacian(nuEff,U) Gauss linear corrected;
    laplacian(nu,U) Gauss linear corrected;
    laplacian(kappaEff,T) Gauss linear limited 0.333;
}

interpolationSchemes
{
    default         linear;
}

snGradSchemes
{
    default         limited 0.333;
}

fluxRequired
{
    default         no;
    p_rgh;
}
// ************************************************************************* //

fvsolution 2

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  1.7.1                                 |
|   \\  /    A nd           | Web:      www.OpenFOAM.com                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      fvSchemes;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

ddtSchemes
{
    default         Euler;
}

gradSchemes
{
    default         Gauss linear;
}

divSchemes
{
    default         none;

    div(phi,U)      Gauss upwind;
    div(phi,T)      Gauss upwind;
    div(phi,k)      Gauss upwind;
    div(phi,epsilon) Gauss upwind;
    div(phi,R)      Gauss upwind;
    div(R)          Gauss linear;
    div((nuEff*dev(T(grad(U))))) Gauss linear;
}

laplacianSchemes
{
    default         Gauss linear uncorrected;
}

interpolationSchemes
{
    default         linear;
}

snGradSchemes
{
    default         uncorrected;
}

fluxRequired
{
    default         no;
    p_rgh;
}
// ************************************************************************* //

5 also tried changing northogonal correctors as per the suggestion in a post by Hjasak up to 4.
In all these cases I find no difference in the initial p_rgh residual. The values follow the same trend as above.


It would be great if some suggestions could be provided on how to approach it.

[MaryBau]

Hi Manu,

Did you find a solution? I am having exactly the same problem that you described and I have not been able to find a solution.

I found this post that talks about the same issue, but no solution yet:

How to use PIMPLE properly?

Cheers,

Mary

[manuc]

Originally Posted by MaryBau

Hi Manu,

Did you find a solution? I am having exactly the same problem that you described and I have not been able to find a solution.

I found this post that talks about the same issue, but no solution yet:

How to use PIMPLE properly?

Cheers,

Mary

I use piso now with Gamg..in most cases it serves the purpose.

[MaryBau]

mmm.... I have been using GAMG, but I still have that problem.

This is what I normally use:

"(p|p_rgh)"
{
      solver          GAMG;
      tolerance      1e-6;
      relTol            0.01;
      smoother      DICGaussSeidel;
      minIter          1;
      maxIter         100;
      nPreSweeps      1;
      nPostSweeps    3;
      nFinestSweeps  3;
      scaleCorrection true; 
      directSolveCoarsest     false; 
      cacheAgglomeration     on; 
      nCellsInCoarsestLevel  50; 
      agglomerator    faceAreaPair; 
      mergeLevels    1;
}

I have tried modifying some of those values, but 1) I have to admit that I do not understand what all those parameters do, 2) I have not seen a difference in the simulation output.

What parameters do you use for GAMG?

Thanks for your help!